rt2x00: rt2800lib: fix default TX power check for RT55xx

The code writes the default_power2 value into the TX field
of the RFCSR50 register, however the condition in the if
statement uses default_power1. Due to this, wrong TX power
value might be written into the register.

Use the correct value in the condition to fix the issue.

Compile tested only.

Signed-off-by: Gabor Juhos <juhosg@openwrt.org>
Cc: stable@vger.kernel.org # 3.10
Acked-by: Gertjan van Wingerde <gwingerde@gmail.com>
Signed-off-by: John W. Linville <linville@tuxdriver.com>