Use explicit .c_str() for hidl_string

hidl_string no longer will provide an implicit cast to const char* as it
interfers with other expected behaviors of the class.  It now emulated
std::string in requiring a call to .c_str() to get the same behavior.

Bug:  36532780
Test:  Build the tree
Change-Id: I265590c7c18f425e44863df062a56b67519a932a
diff --git a/drm/1.0/default/CryptoPlugin.cpp b/drm/1.0/default/CryptoPlugin.cpp
index 9c51b15..5e5b5a7 100644
--- a/drm/1.0/default/CryptoPlugin.cpp
+++ b/drm/1.0/default/CryptoPlugin.cpp
@@ -35,7 +35,7 @@
     // Methods from ::android::hardware::drm::V1_0::ICryptoPlugin follow
     Return<bool> CryptoPlugin::requiresSecureDecoderComponent(
             const hidl_string& mime) {
-        return mLegacyPlugin->requiresSecureDecoderComponent(mime);
+        return mLegacyPlugin->requiresSecureDecoderComponent(mime.c_str());
     }
 
     Return<void> CryptoPlugin::notifyResolution(uint32_t width,