wifi: rtlwifi: 8192d: initialize rate_mask in rtl92de_update_hal_rate_mask()

le32p_replace_bits() only updates partial bits of rate_mask, and GCC warns
below. Set initial value to avoid warnings, and prevent random value of
missed bits (bit 6 of rate_mask.macid_and_short_gi).

In file included from ./include/linux/fortify-string.h:5,
                 from ./include/linux/string.h:369,
                 from ./include/linux/bitmap.h:13,
                 from ./include/linux/cpumask.h:13,
                 from ./include/linux/sched.h:16,
                 from drivers/net/wireless/realtek/rtlwifi/rtl8192d/../wifi.h:9,
                 from drivers/net/wireless/realtek/rtlwifi/rtl8192d/hw_common.c:4:
In function 'le32p_replace_bits',
    inlined from 'rtl92de_update_hal_rate_mask.isra' at drivers/net/wireless/realtek/rtlwifi/rtl8192d/hw_common.c:986:2:
./include/linux/bitfield.h:189:15: warning: 'rate_mask' is used uninitialized [-Wuninitialized]
  189 |         *p = (*p & ~to(field)) | type##_encode_bits(val, field);        \
      |               ^~
./include/linux/bitfield.h:196:9: note: in expansion of macro '____MAKE_OP'
  196 |         ____MAKE_OP(le##size,u##size,cpu_to_le##size,le##size##_to_cpu) \
      |         ^~~~~~~~~~~
./include/linux/bitfield.h:201:1: note: in expansion of macro '__MAKE_OP'
  201 | __MAKE_OP(32)
      | ^~~~~~~~~
drivers/net/wireless/realtek/rtlwifi/rtl8192d/hw_common.c: In function 'rtl92de_update_hal_rate_mask.isra':
drivers/net/wireless/realtek/rtlwifi/rtl8192d/hw_common.c:863:37: note: 'rate_mask' declared here
  863 |         struct rtl92d_rate_mask_h2c rate_mask;
      |                                     ^~~~~~~~~

Compile tested only.

Fixes: 014bba73

 ("wifi: rtlwifi: Adjust rtl8192d-common for USB")
Cc: Bitterblue Smith <rtl8821cerfe2@gmail.com>
Signed-off-by: Ping-Ke Shih <pkshih@realtek.com>
Link: https://msgid.link/20240504111916.31445-1-pkshih@realtek.com