staging: rtlwifi: phydm: Remove useless parentheses

Remove unnecessary parentheses to comply with preferred coding style for
the linux kernel and avoid the following checkpatch's message:
'CHECK: Unnecessary parentheses around'.

Credits to checkpatch.

Signed-off-by: Frank A. Cancio Bello <frank@generalsoftwareinc.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>