ARM: dts: apq8064: Prefix the gsbi6 uart pins correctly

Usage of generic names like "uart_pins" is confusing to the reader, given
the fact that there could be more than one uart on APQ8064.
This patch adds gsbi prefix to uart pinctrl nodes so as to avoid such
confusion.

Signed-off-by: Srinivas Kandagatla <srinivas.kandagatla@linaro.org>
Signed-off-by: Andy Gross <agross@codeaurora.org>