tty: serial: amba-pl011: fix formatting of conditions

Fix the following checkpatch warnings & checks:

	$ ./scripts/checkpatch.pl --strict --file \
        drivers/tty/serial/amba-pl011.c

    CHECK: Unbalanced braces around else statement
    CHECK: Unnecessary parentheses around '[...]'
    CHECK: braces {} should be used on all arms of this statement
    CHECK: Comparison to NULL could be written "[...]"
    WARNING: Comparisons should place the constant on the right side of the test

Reviewed-by: Linus Walleij <linus.walleij@linaro.org>
Signed-off-by: Théo Lebrun <theo.lebrun@bootlin.com>
Link: https://lore.kernel.org/r/20231207-mbly-uart-v6-5-e384afa5e78c@bootlin.com


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