ARM: SAMSUNG: serial: Fix on handling of one clock source for UART

This patch fixes the way of comparison for handling of two or more
clock sources for UART.

For example, if just only one clock source is defined even though
there are two clock sources for UART, the serial driver does not
set proper clock up. Of course, it is problem.

So this patch changes the condition of comparison to avoid useless
setup clock and adds a flag 'NO_NEED_CHECK_CLKSRC' which means
selection of source clock is not required.

In addition, since the Exynos4210 has only one clock source for UART
this patch adds the flag into its common_init_uarts().

Signed-off-by: Boojin Kim <boojin.kim@samsung.com>
Signed-off-by: Kukjin Kim <kgene.kim@samsung.com>
Cc: stable <stable@kernel.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@suse.de>