ARM: sharpsl_param: work around -Wstringop-overread warning

gcc warns that accessing a pointer based on a numeric constant may
be an offset into a NULL pointer, and would therefore has zero
accessible bytes:

arch/arm/common/sharpsl_param.c: In function ‘sharpsl_save_param’:
arch/arm/common/sharpsl_param.c:43:9: error: ‘memcpy’ reading 64 bytes from a region of size 0 [-Werror=stringop-overread]
   43 |         memcpy(&sharpsl_param, param_start(PARAM_BASE), sizeof(struct sharpsl_param_info));
      |         ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

In this particular case, the warning is bogus since this is the actual
pointer, not an offset on a NULL pointer. Add a local variable to shut
up the warning and hope it doesn't come back.

Signed-off-by: Arnd Bergmann <arnd@arndb.de>
Acked-by: Daniel Mack <daniel@zonque.org>
Cc: Daniel Mack <daniel@zonque.org>
Cc: Haojian Zhuang <haojian.zhuang@gmail.com>
Cc: Robert Jarzmik <robert.jarzmik@free.fr>
Cc: Russell King <linux@armlinux.org.uk>
Cc: Linus Walleij <linus.walleij@linaro.org>
Link: https://gcc.gnu.org/bugzilla/show_bug.cgi?id=99578
Link: https://lore.kernel.org/r/20210927145332.2784005-1-arnd@kernel.org'
Signed-off-by: Arnd Bergmann <arnd@arndb.de>