auxdisplay: charlcd: deduplicate simple_strtoul()

auxdisplay: charlcd: deduplicate simple_strtoul()

Like in commit 8b2303de399f ("serial: core: Fix handling of options
after MMIO address") we may use simple_strtoul() which in comparison to
kstrtoul() can do conversion in-place without additional and unnecessary
code to be written.

Link: http://lkml.kernel.org/r/20190801192904.41087-2-andriy.shevchenko@linux.intel.com
Signed-off-by: Andy Shevchenko <andriy.shevchenko@linux.intel.com>
Reviewed-by: Petr Mladek <pmladek@suse.com>
Cc: Geert Uytterhoeven <geert+renesas@glider.be>
Cc: Mans Rullgard <mans@mansr.com>
Cc: Miguel Ojeda <miguel.ojeda.sandonis@gmail.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>