staging: rtl8723bs: Fix checkpatch.pl warnings

This patch resolves coding style brace warning and constant on right warning.
WARNING: Comparisons should place the constant on the right side of the test
WARNING: braces {} are not necessary for single statement blocks
CHECK: Comparison to NULL could be written "!pbuf"

Signed-off-by: Vandana BN <bnvandana@gmail.com>
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 v2- Edited commit message and subject
 v3- Edited commit message
 v4- changed NULL check to use !pbuf
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Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>