mfd: don't export wm3850 static functions

mfd: don't export wm3850 static functions

October 10th linux-next build (powerpc allyesconfig) failed like this:

drivers/mfd/wm8350-core.c:1131: error: __ksymtab_wm8350_create_cache causes a section type conflict

Caused by commit 89b4012befb1abca5e86d232bc0e2a797b0d9825 ("mfd: Core
support for the WM8350 AudioPlus PMIC"). wm8350_create_cache is not used
elsewhere, so remove the EXPORT_SYMBOL.

Signed-off-by: Stephen Rothwell <sfr@canb.auug.org.au>
Signed-off-by: Mark Brown <broonie@opensource.wolfsonmicro.com>
Signed-off-by: Samuel Ortiz <sameo@openedhand.com>