earlycon: Increase options size

Now that the clock frequency is also part of the options, 16 bytes is
too little.

Without this patch dmesg does not show the whole options, Eg:

earlycon: uart0 at MMIO32 0x00000000fedc9000 (options '115200n8,480000')

instead of: '115200n8,48000000'

Signed-off-by: Ricardo Ribalda <ribalda@chromium.org>
Reviewed-by: Jiri Slaby <jirislaby@kernel.org>
Link: https://lore.kernel.org/r/20221123-serial-clk-v3-2-49c516980ae0@chromium.org


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