staging: rtl8712: simplify control flow

The function iterates an index from 0 to NUM_PMKID_CACHE and returns
the first index for which the condition is true. If no such index is
found, the function returns -1. Current code has a complex control
flow that obfuscates this simple task. Replace it with a loop.

Also, given the shortened function body, replace the long variable
name psecuritypriv with a short variable name p.

Reported by checkpatch:

WARNING: else is not generally useful after a break or return

Signed-off-by: Sevinj Aghayeva <sevinj.aghayeva@gmail.com>
Link: https://lore.kernel.org/r/20220403165325.GA374638@euclid


Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>