staging: rtlwifi: phydm: phydm_adc_sampling.c Remove brackets

Remove parentheses around right hand side of expression. Issue found
with Coccinelle.

Signed-off-by: Nishka Dasgupta <nishka.dasgupta@yahoo.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>