[PATCH] button: add udevice forward declaration

[Neil Armstrong]

After 401d1c4f5d2d ("common: Drop asm/global_data.h from common header")
build fails with :

drivers/button/button-uclass.c:13:5: error: conflicting types for 'button_get_by_label'
int button_get_by_label(const char *label, struct udevice **devp)
    ^~~~~~~~~~~~~~~~~~~

Adding struct udevice forward declaration in button.h solves the build error.

Fixes: 401d1c4f5d2d ("common: Drop asm/global_data.h from common header")
Suggested-by: Heinrich Schuchardt <xypron.glpk at gmx.de>
Signed-off-by: Neil Armstrong <narmstrong at baylibre.com>
---
Hi,

This is needed to fix build on vim3/vim3l after [1] is applied.

[1] https://patchwork.ozlabs.org/project/uboot/cover/20210218103318.18915-1-m.szyprowski@samsung.com/

 include/button.h | 2 ++
 1 file changed, 2 insertions(+)

diff --git a/include/button.h b/include/button.h
index 688b63b082..ee14fadf0c 100644
--- a/include/button.h
+++ b/include/button.h
@@ -6,6 +6,8 @@
 #ifndef __BUTTON_H
 #define __BUTTON_H
 
+struct udevice;
+
 /**
  * struct button_uc_plat - Platform data the uclass stores about each device
  *
-- 
2.25.1