pcmcia: soc_common: restore previous socket state on error

If an attempt to set a socket state returns an error, restore the
previous socket state.  If restoring the previous socket state
fails, warn about this.

This allows us to have simple error handling in the socket state
configuration handlers - there is no need for every handler
implementation to manually undo the updates, which can be complex
when regulators are involved.

Signed-off-by: Russell King <rmk+kernel@armlinux.org.uk>