rtc: davinci: remove incorrect reference to probe function

The davinci rtc driver uses the module_platform_driver_probe()
helper to call the probe function and mark it as __init, but
it also puts a reference into its davinci_rtc_driver function.

This will crash if we ever get a deferred probe and the probe
function is called again after the init section has been removed.
kbuild warns about this:

WARNING: vmlinux.o(.data+0x1aa2b4): Section mismatch in reference from the variable davinci_rtc_driver to the function .init.text:davinci_rtc_probe()
The variable davinci_rtc_driver references
the function __init davinci_rtc_probe()

This patch removes the .probe callback from the platform driver,
which avoids those problems.

Signed-off-by: Arnd Bergmann <arnd@arndb.de>
Signed-off-by: Alexandre Belloni <alexandre.belloni@free-electrons.com>