gpio: sprd: Add missing break in switch statement

Fix the following warning by adding a missing break:

drivers/gpio/gpio-eic-sprd.c: In function ‘sprd_eic_irq_set_type’:
drivers/gpio/gpio-eic-sprd.c:403:3: warning: this statement may fall through [-Wimplicit-fallthrough=]
   switch (flow_type) {
   ^~~~~~
drivers/gpio/gpio-eic-sprd.c:435:2: note: here
  default:
  ^~~~~~~

This patch is part of the ongoing efforts to enable
-Wimplicit-fallthrough.

Signed-off-by: Gustavo A. R. Silva <gustavo@embeddedor.com>
Reviewed-by: Baolin Wang <baolin.wang@linaro.org>
Signed-off-by: Linus Walleij <linus.walleij@linaro.org>