Revert "thunderbolt: Prevent crash if non-active NVMem file is read"

This reverts commit 03cd45d2.

Commit 664f0549 ("nvmem: core: use is_bin_visible for permissions")
incidentally adds support for write-only nvmem. Hence, this workaround
is no longer required, so drop it.
Signed-off-by: Nicholas Johnson <nicholas.johnson-opensource@outlook.com.au>
Signed-off-by: Mika Westerberg <mika.westerberg@linux.intel.com>

drivers/thunderbolt/switch.c

@@ -348,12 +348,6 @@ static int tb_switch_nvm_read(void *priv, unsigned int offset, void *val,
 	return ret;
 }
 
-static int tb_switch_nvm_no_read(void *priv, unsigned int offset, void *val,
-				 size_t bytes)
-{
-	return -EPERM;
-}
-
 static int tb_switch_nvm_write(void *priv, unsigned int offset, void *val,
 			       size_t bytes)
 {
@@ -399,7 +393,6 @@ static struct nvmem_device *register_nvmem(struct tb_switch *sw, int id,
 		config.read_only = true;
 	} else {
 		config.name = "nvm_non_active";
-		config.reg_read = tb_switch_nvm_no_read;
 		config.reg_write = tb_switch_nvm_write;
 		config.root_only = true;
 	}