staging: rtlwifi: Remove function that only returns the second argument

Because the odm_signal_scale_mapping function is only called to return the
second argument, remove the unnecessary function and change the statements
that call it, including removing unneeded braces and adding a blank line.

Note that removing casts (u8 to s32 and back to u8) will not lose
information because the value converted should be between 0 and 100.

Signed-off-by: Maya Nakamura <m.maya.nakamura@gmail.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>